PROVIDENCE, R.I. — Just before Thanksgiving, Claudio Neves Valente checked into a hotel in Boston and repeatedly visited Brown University, where he studied physics 25 years earlier. On December 13, he launched a violent attack in a lecture hall, killing two students and injuring nine others before fleeing the scene. Two days later, Valente fatally shot a Massachusetts professor, Nuno F.G. Loureiro, who was a classmate from Portugal. Investigators are piecing together Valente's whereabouts leading up to the attacks and have released surveillance footage in hopes of gathering more information. The new details have left the university community grappling with this devastating act of violence.